Field of Invention
The present invention relates to a packet transmission method. More particularly, the present invention relates to a transmission method for a Control and Provisioning of Wireless Access Point (CAPWAP) packet in a wireless distribution system.
Description of Related Art
In a wireless distribution system (WDS), wireless connections can be established through multiple wireless access points (AP), so as to extend a distribution range or coverage of the wireless network. When a new wireless access point is to be added into or joined the wireless distribution system, a wireless distribution connection has to be configured before a CAPWAP authentication is performed. Then, a CAPWAP packet is transmitted to each wireless access point through the wireless distribution connection.
CAPWAP is a specification (RFC 5415 and 5416) developed by Internet Engineering Task Force (IETF) based on a connection technology of Ethernet. It defines a communication standard of a wireless local area network access controller (AC) capable of managing a group of wireless access points in a 802.11 wireless network environment. Because the protocol operates based on Internet Protocol (IP) and User Datagram Protocol (UDP), it is required to obtain an IP address and establish a connection to the internet before the wireless access points operate based on the protocol.
However, CAPWAP operates according to UDP based on Ethernet, and UDP only provides unreliable transmissions. Therefore, when a packet is lost in the wireless transmission environment, CAPWAP cannot identify the cause of losing the packet so that operations related to CAPWAP such as addition, identification and control management of access points cannot be performed.
For example, for a management of a controlling channel between the access controller and the wireless access point, if a packet is destroyed due to interference or collision when the wireless access point transmits an echo request message to the access controller, then the controller may determine that the wireless access point is not found or is damaged, and may set a connection state of the wireless access point as off-line because CAPWAP cannot identify the cause of losing the packet. Thus, when CAPWAP operates in the wireless distribution system, if a new wireless access point is to be added or a related authentication is performed, an error is likely to occur because the packet is likely to be lost.
Therefore, under the condition that the packet is likely to be erroneous in the wireless distribution system, how to prevent the CAPWAP packet from being lost becomes a problem to be solved in the industry.